High-frequency amplifier apparatuses are used for generating power that is suitable for exciting plasma. In these apparatuses, it is known to use transistors, such as bipolar transistors or Laterally Diffused metal Oxide Semiconductor (LDMOS) transistors. For plasma excitation, it is desirable to operate the high-frequency amplifier apparatus in class F or inverse class F amplifier operation.
But in these cases, a significant amount of heat may build up. For example, if power is reflected by a load, it converts into heat in the high-frequency amplifier apparatus. Different amplifier apparatuses are disclosed, for example, in the following documents: US 2009/0027936 A1, US 2010/0148866 A1, U.S. Pat. Nos. 7,221,102 B2, 5,835,367 A, US 2008/0272875 A1 and US 2013/0038226 A1.